Converter



July 23, 194 6. Y TlLLMAN 2,404,669

' CONVERTER r Filed Sept. 25, 194% 2 Sheets-Sheet 1 COUPLING FORIF FEED BACK. CO/LS 17 AND I4- COUPLED FOE OSCJ-EEDBACK SEE FIG.E

TO 62/05/45 I VOLTAGE 3/ Pi Z.

26 5 Hand /7 His Attorney.

July 23, 1946. J. E. TILLMAN 2,404,559

' CONVERTER Filed Sept. 25, 1942 I 2 Sheets-Sheet 2 Fig.3

/NPUT TRANSFORMER GAIN CON VE/Z TER GAIN GA IN OVERA L L GAIN Fig.5.

W/Th REGENERATION WITHOUT REGENERATION ATTfNl/A now FREQUENCY INTERMEDIATE FREQUE/YC Y CIRCUIT GAIN WI TH DEGENERATlU/V ANTENNA GAIN GAI/V FREQUENCY q l n h;

JoFmn E.Til lman,

c: JA 1 Patented July 23, 1946 CONVERTER John E. Tillman, Stratford, Conn, assignor to General Electric Company, acorporation of New York Application September 25, 1942, Serial No. 459,605

12 Claims. 1.

My invention relates to converters such as are used in superheterodyne receivers, and it has for one of its objects toeffect certainimprovernents therein with respect to control of the gain had insuch converters.

When employed. in receivers for broadcast reception, as. in. household receivers, the signal input circuit and local oscillator circuit are tunable over corresponding ranges of frequency. The input circuit may be tunable, for examplafrom 550 kilocycles to 1700 kilocycles and the local oscillator from. 1005 kilocycles to 2155 kilocycles giving a fixed intermediate frequency of 455 kilocycles.

It is desired in such receivers that the intensity of the intermediate frequency oscillations be constant throughout the range of such tuning.

An object of my invention is to provide improved means to reduce variations in the intensity of the intermediate frequency oscillations as the tuning of the circuit is varied.

A further object. of my invention is to provide improved means to vary the gain had in the converter in a way. to. compensate for variations in gain had inthe input circuit when the tuning is varied.

A further object of my invention is to utilize the. efiects of regeneration or degeneration as desired to effect, such compensation and to vary such effects automatically with tuning.

Another object of my invention is to provide such means without materially increasing the cost. of. the apparatus or complicating its adjustment.

The. novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which Fig. 1 represents a diagram of an embodiment of my invention; Fig. 2 represents a plan view showing the relative arrangement of certain coils thereof; Figs. 3, 4 and 6 represent certain graphs illustrating gain characteristics of my invention; Fig. represents certain graphs illustrating selectivity characteristics of my invention, and Fig. 7 is a diagram of a modified circuit.

Referring to Fig. l of the drawings, I have shown therein an electron discharge device I having a cathode. 2, control electrode 3, a screen electrode 4, afurther control electrode 5, a further screen electrode 6, a. suppressor electrode 1 and an anode 8. Radio frequency oscillations to be converted by the discharge device I may be intercepted by means of an antenna 9 and supplied between the control electrode 5 and cathode 2 by means of a coupling comprising condenser is and coils Hand F2. The coils II and I2 are connected in series between the controlelectrode 5 and the cathode through a condenser l3 and an inductance coil M, and the antenna 9 is connected through condenser [0 at a point between coils H. and I2 whereby the coils H and I2. act as an autotransformer stepping up the oscillations received on the antenna 9 and impressing them between the control electrode 5 and the.

cathode. The input circuit of the converter comprising coils II and I2 may be tuned to the frequency of oscillations to be received by means of a variable tuning condenser l5. If desired, this condenser may be shunted by means of trimming condenser l6, as is common in the practice of such devices.

The local oscillator-of this converter comprises a tuned frequency determining circuit including inductance l4 and inductance ll across which is connected a tuning condenser 18, the latter of which may also be shunted by a trimming condenser l9. The tuning condenser I8 maybe unicontrolled with the condenser l5 in the usual way, as indicated by the dotted lines at 20. The cathode 2 of the discharge device is connected to a point intermediate the inductances l4 and IT,

one terminal of the frequency determining circuit being connected to the control electrode 3 through the usual grid leak 21 and grid condenser 22, these elements being proportionedto provide a suitable operating bias upon the control electrode 3. The opposite terminal of the frequency determining circuit is connected through by-pass condenser 23 to. the screen electrodes 4 and B of the discharge device.

Thus, the circuit [4, l1, I8 and is having its intermediate point connected to the cathode, and having one terminal connected to the screen electrode and the other to the control electrode, provides the required feedback between the screen electrode 4 acting as an anode and the control electrode 3 to support oscillations in the local oscillating circuit. These oscillations have their frequency controlled by the tuning condenser l8. Such oscillations combine with the oscillations received by the antenna 9 in the converter to produce oscillations in the output circuit of the discharge devicel having a frequency equal to the 3 difference in the frequency of the local oscillations and the received signals.

This output circuit comprises the primary winding 24 of an intermediate frequency transformer, which is tuned to the frequency of the intermediate frequency oscillations by means of a trimming condenser 25. The secondary winding 26 of this transformer is also tuned to the same frequency by means of condenser 21. Oscillations supplied through the transformer 24,

26 may be amplified and ultimately rectified to reproduce the modulations present thereon which, of course, may be of voice or music frequency or other type of signal as desired,

Anode operating potential for the discharge device may be supplied across by-pass and smoothing condenser 23 as indicated by the plus and minus signs shown on the drawings, the

negative terminal of this sourcebeing grounded as indicated at 3!]. Suitable bias for the c0ntrol electrode 5 of the discharge device may be supplied through conductor 31 and resistance 32. This conductortl may extend to the output of a signal rectifier in the receiver and have impressed thereon anegative unidirectional voltage varying in intensity with the intensity of the received signals thereby to produce automatic volume control. The resistance 32 is proportioned with respect to condenser l3 to act as a filter to suppress any audio frequency variations which may appear in the bias voltage supplied by conductor 31. This bias voltage is also supplied over conductor 33 through the secondary winding of transformer 24, 26 to the input electrode of a subsequent amplifier which may be connected to receive oscillations from the transformer 24, 26.

. .In accordance with my invention, the windings l4, l1 and 24 may be arranged in inductive relation with each other so that oscillations of theintermediate frequency present in the winding 24 are induced in the windings l4 and I1 and are thus impressed upon the input electrode 3, of the discharge device. To this end these windings may be arranged coaxially on a single form 28 as shown in'Fig. 2. Thus the oscillatfling circuit I4, H, l8 and I9 and the coupling between inductances l4, l1 and 24 serves as a feedback path for the converter operable at the intermediate frequency to produce regeneration, or degeneration, as may be desired in accordance with the polarity of the coupling. The extent of such regeneration or degeneration is, of course, dependent upon the efiiciency with which oscillations of the intermediate frequency are supplied through the circuit I4, l1, l8, IE! to the input of the discharge device, and this transmission efiiciency, in turn, is, of course, dependent upon the frequency to which the local oscillating circuit is tuned. That is, the transmission efficiency of this oscillating circuit at the intermediate frequency varies as the tuning of this circuit is varied from one end of its tuning range to the other. This variation in transmission emciency may be taken advantage of to control the regeneration or degeneration to an extent sufficient to compensate for variation in the transmission efiiciency of the input system comprising antenna 9, condenser l0, and windings II and I2, thereby to reduce variations in the intensity of intermediate frequency oscillations in transformer 24, 26 ,with variation in the tuning of the receiver.

For example, the input circuit ll, I2, I5, l6 may be tunable over a range extending from 550 kilocycles to 1700 kilocycles if the receiver be one used for ordinary home broadcast reception, for example, and the local oscillator circuit l4, l1, l8, l9 may be tunable in unison therewith over a range extending from 1005 kilocycles to 2155 kilocycles giving a fixed intermediate frequency in transformer 24, 26 of 455 kilocycles throughout the range. Winding l2 may tune with the capacity across it at a frequency above 1700 kilocycles with the result that the transmission efficiency of the input circuit increases as the frequency to which the circuit tunes is increased. At the same time, the circuit l4, ll, l8, I9 is tuned to a frequency increasingly removed from the intermediate frequency 455 kilocycles and thus its transmission efiiciency to intermediate frequency currents is progressively reduced. These opposite effects tend to maintain a constant intensity of oscillation in the transformer 24, 26 throughout the tuning range.

This effect is illustrated in Fig. .3, the curves of which represent gain, plotted as ordinates against frequency to which the receiver is tuned plotted as abscissa. The curve A represents the gain of the input system between antenna Band the control electrode 5. It will be seen that it rises steadily with increase in frequency throughout the frequency range to which the receiver is tunable.

Curve B represents the gain in the converter itself and it will be seen that it decreases with increase in the frequency to which the receiver is tunable. This is brought about by reason of the reduced regeneration secured by reason of reduced transmission of the intermediate frequency oscillations through the circuits of the local oscillator to the input of the converter as the frequency of the local oscillator is increased.

Curve C represents the gain of the receiver between antenna 8 and transformer 24, 26. It

will be seen that this gain is substantially. constant throughout the frequency range.

Fig. 4 represents certain sensitivity characteristics pertaining to my invention, these curves showing the relation betweenthe input voltage necessary to produce a constant output from the system and the frequency to which the receiver is tuned. The curve D represents the character istics secured by the use of regeneration supplied through the circuits of the local oscillator as previously described. This curve is substantially flat, indicative of constant sensitivity of the receiver throughout the tuning range. Curve E represents the sensitivity without regeneration. It will be seen that this curve rises toward the lower frequency, indicating reduced sensitivity at the lower frequencies.

Regeneration, employed as provided in accordance with my invention, also has the effect of very materially increasing the selectivity of the system. Fig. 5 represents certain characteristics showing this increased selectivity secured by my invention. These curves are plotted in terms of variation of the intermediate frequency from 455 kilocycles ineither direction over 'a range of 20 kilocycles plotted against attenuation as .ordi nates. Curves F represent the attenuation of the converter as the intermediate frequency is varied from 455 kilocycles in either direction over the range of 20 kilocycles, these curves corresponding to the condition when regeneration is .provided in accordance with my invention. Curves G, on the other hand, correspond to the selectivity present when no regeneration is employed.

It will be seen that the attenuation with variation-in frequency is very greatlyincreased by the presence of the regeneration.

Of course, ifdesired, the oscillations supplied back to th input circuit from the output circuit may be supplied in degenerative phase rather than regenerative phase. The effect of such degeneration up the selectivity of th receiver is the opposite of that produced by regeneration and tends to broaden the band width of oscillations transmitted through the system.

This degeneration also 'has'the opposite effect with respect to control of the gain of the converter, increasingthegain as the frequency is increased. This is shownby'the curve H of Fig. 6, which shows the gain of the receiver plott d as ordinates against frequency plotted as abscissa. Such a characteristic may be advantageous in a receiver in which the input circuit has a gain characteristic such as that indicated at I in Fig. 6. This may occur if the winding l2, for example, be one having a natural frequency below 550 kilocycles.

The feedback from transformer 2d, 25 through windings I1 and Hi to the input of the discharge device may be secured capacitively rather than inductively as illustrated in Fig. 7. Fig. '7 is similar to Fig. 1 but diifers therefrom in that capacitance 34 is shown connected between the upper terminals of coils 24 and H for capacitive feedback. This capacitance may be a condenser connected as shown or may comprise the inherent capacity between coils 24, H and i i. ese coils may be poled so that such feedback is degenerative orregenerative as desired.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto since various modifications both in th circuit arrangement and in the instrumentalities employed may be made, and I contemplate by the appended claims to cover such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

'1. The combination, in a superheterodyne receiver, of a signal input circuit; a locally excited oscillatory circuit, a converter having an intermediate frequency output circuit, means to supply I oscillations from said signal input circuit and from said locally excited oscillatory circuit to said converter to beat in said converter to produce oscillations of intermediate frequency in said intermediate frequency output circuit, and means to control the gain between said signal input circuit and said intermediate frequency output circuit, said means comprising means to supply oscillations of said intermediate frequency to said cally excited oscillatory circuit and thence to said converter in phase to produce desired control of the gain of said converter.

2. The method of controlling the gain of a superheterodyne converter which produces oscillations of intermediate frequency from signal oscillations combined with oscillations supplied thereto from a local oscillator which comprises supplying oscillations of said intermediate frequency to said local oscillator and thence to said converter in such phase and intensity as to produce desired control of said gain.

3. The method of controllin the gain of a superheterodyne converter which produces oscillations of intermediate frequency from signal oscillations combined with oscillations supplied thereto from a local oscillator which comprises supplying oscillations of said intermediate frequency to said local oscillator and thence to said converter in such phase and intensity as to produce desired control of said gain and varying the intensityof "oscillations of said intermediat frequency supplied through said local oscillator to saidconverter 'by varying the frequency of the oscillations produced'bysaid local oscillator.

4. The combination, in a superheterodyne receiver, of a converter having 'an output circuit tuned toth'e intermediate frequency to be produced, a local oscillatorhaving-afrequency determiningcircuit, a signal inputcircuit, said signal input circuitand "local oscillator beingtunable over respective ranges and being connected to supply oscillations to said converter of frequency different by the amount of said intermediate frequency, and a "feedback path for said converter for currents -of said intermediate frequency, said path extending from said output circuit to said frequency determining circuit and thence to said converter, said feedback path'including said frequency determining circuit, andmea'ns to supply said intermediate frequency oscillations to said converter in 'such 'ph'a'se relation to said intermediate frequency oscillations in said output ciif cuit as to produce desired change in gain of said converter with variation in tuning of 'saidsiiial input circuit and local oscillator 'o'ver said'ra'nges.

" frequency determining circuit beingtuned to frequences different by said 'i'ntermedate frequency and being tunable over corresponding ranges of frequency, a feedback path for said converter comprising a coupli'ngffor osciuauonsdr intermediate frequency between said output circuit and said frequency determining circuit whereby oscillations of said intermediate frequency are supplied through said coupling and said frequency determining circuit to said converter to control the gain thereof, and the intensity of said feedback os'cillationsis varied by the tuning of said frequency determining circuit, said feedback path being constructed and'arranged to supply said intermediate frequency oscillations in such phase relation to said intermediate frequency oscillations in said output circuit as to produce desired control of the gain of said converter with said variation in tuning of "said frequency determining circuit.

6. In a converter for superheterodyne receivers having a local oscillator circuit tunable over a range of frequencies and an output circuit tuned to a fixed frequency, the method of controlling the gain of said converter which comprises supplying oscillations of said fixed frequency from said output circuit to said tunable local oscillator circuit for transmission to said converter with the local oscillations generated thereby and regulating the intensity of said fixed frequency oscillations so transmitted by varying the tuning of said local oscillator over said range to produce desired gain of said converter over a range of frequencies corresponding to the tuning range of said local oscillator circuit.

7. The combination, in a superheterodyne receiver, of a converter having an output circuit for currents of intermediate frequency, a signal input circuit and a local oscillator circuit tuned to frequencies different by said intermediate frequency and tunable over respective ranges, the

efiiciency of transmission through said input circuit varying from one end of said range to the other, afeedback path" for currents of intermediate frequency including said local oscillator circuit and a coupling from said output circuit to said local oscillation circuit, the efiiciency of transmission of currents of intermediate frequency'through said path varying with the tuning of said local oscillator over said range, said variations in transmission being proportioned relative to each other to reduce variation in the intensity of intermediate frequency oscillations in said output circuit during tuning of said input and local oscillator circuits over said ranges.

8. The combination, in a superheterodyne receiver, of a signal input circuit, a local oscillator circuit, a converter having an intermediate frequency output circuit, means to supply oscillations from said input circuit and local oscillator circuit to said converter, means to supply oscillations of said intermediate frequency from said output circuit through said local oscillator circuit to said converter in regenerative phase, and means to vary the tuning of said signal input circuit and said local oscillator circuit in unison to maintain constant said intermediate frequency and simultaneously to vary oppositely the transmission efiiciency of said input circuit to signal currents and that of said local oscillator circuit to intermediate frequency currents thereby to maintain currents of said intermediate frequency of constant intensity.

9. The combination, in a superheterodyne receiver, of a signal input circuit, a local oscillator circuit, a converter having an intermediate frequency output circuit, means to supply oscillations from said input circuit and local oscillator circuit to said converter, means to supply oscillationsof said intermediate frequency from said output circuit through said local oscillator circuit to said converter in degenerative phase, and means to vary the tuning of said signal input circuit and said local oscillator circuit in unison to maintain constant said intermediate frequency and simultaneously to vary oppositely the transmission effi'ciency of said input circuit to, signal currents and that of said local oscillator circuit to intermediate frequency currents thereby to maintain currents of said intermediate frequency of constant intensity.

10. The combination, in a superheterodyne receiver, of a signal input circuit, a local oscillator circuit, a converter having an input circuit and an intermediate frequency output circuit, means to supply oscillations from said signal input circuit and local oscillator circuit to the input of said converter, and means to supply oscillations of said intermediate frequency from said output a circuit to said local oscillator circuit and thence to said converter with intensity to produce desired selectivity of said receiver. u

11. The combination, in a superheterodyne receiver, of an electron discharge device having an anode, a cathode, and a plurality of control electrodes-an output circuit between said anode and cathode, an oscillatory circuit connected to said cathode and at least one of said control electrodes to have oscillations excited therein, an input circuit connected between one of said control'electrodes and said cathode and tuned to a frequcncy different from the frequency to which said oscillatory circuit is tuned, means to vary the tuning of said input circuit and oscillatory circuit over corresponding ranges of frequencies in unison, whereby oscillations of intermediate frequency are produced in said output circuit, said'oscillations of intermediate frequency being subject to variation in intensity with said variation in tuning, and a feedback path for oscillations of said intermediate frequency including said oscillatory circuit, said path being so poled with respect to said intermediate frequency and so affected by said variation in tuning of said oscillatory circuit as to reduce said variation in intensity of said intermediate frequency oscillations with variation in said tuning.

12. The combination, in a superheterodyne receiver, of a pentagrid converter having an output circuit, a tuned signal input circuit, and a local oscillatory circuit all connected to respective electrodes thereof, said converter exciting oscillations in said oscillatory circuit to be combined with oscillations received in said input circuit to produce intermediate frequency oscillations in said output circuit, and a coupling for intermediate frequency osoillations between said output circuit and said oscillatory circuit, whereby intermediate frequency oscillations are supplied from said output circuit back through said oscillatory circuit to said converter with intensity varying with the tuning of said oscillatory circuit, means to vary the tuning of said input and oscillatory circuits in unison, said input circuit having gain variable with tuning, the variation in gain of said input circuit and the variation in intensity of said intermediate frequency oscillations supplied back through said oscillatory circuit to said coni verter being so related to each other as to produce desired intensity of oscillations in. said output circuit for all variations in said tuning.

JOHN E. TILLMAN. 

